This is complete garbage OP. Where did you get your 50/60g by level 40 estimate? From your ass, that's where. A clear case of 96.43827% of all statistics are made up on the spot.
My method to make money on the run up to 40 is to grind your levels in an area THEN do the quests when they are green for the rewards. Gathering professions make money too. Sod the manufacturing profs until max level as they usually cost you money to level before then. Grind, grind, grind - loot everything. Vendor all greys (some greys vendor for a surprisingly high amount of silver), auction everything else (use auctioneer add on to get best prices). If you put a bit of effort in then you'll have your mount at 40, no problem.